Persistent unit IDs

core/src/mindustry/io/versions/Save1.java

@@ -0,0 +1,15 @@
+package mindustry.io.versions;
+
+import java.io.*;
+
+public class Save1 extends LegacySaveVersion{
+
+    public Save1(){
+        super(1);
+    }
+
+    @Override
+    public void readEntities(DataInput stream) throws IOException{
+        readLegacyEntities(stream);
+    }
+}